biostudies-literatureUnknown109(37)Kang XThe C-terminal domain (M(pro)-C) of SARS-CoV main protease adopts two different fold topologies, a monomer and a 3D domain-swapped dimer. Here, we report that M(pro)-C can reversibly interconvert between these two topological states under physiological conditions. Although the swapped ?(1)-helix is fully buried inside the protein hydrophobic core, the interconversion of M(pro)-C is carried out without the hydrophobic core being exposed to solvent. The 3D domain swapping of M(pro)-C is activated by an order-to-disorder transition of its C-terminal ?(5)-helix foldon. Unfolding of this foldon promotes self-association of M(pro)-C monomers and functions to mediate the 3D domain swapping, without which M(pro)-C can no longer form the domain-swapped dimer. Taken together, we propose that there exists a special dimeric intermediate enabling the protein core to unpack and the ?(1)-helices to swap in a hydrophobic environment, which minimizes the energy cost of the 3D domain-swapping process.Proceedings of the National Academy of Sciences of the United States of America14900-5https://www.ebi.ac.uk/biostudies/studies/S-EPMC3443179biostudies-literatureFoldon unfolding mediates the interconversion between M(pro)-C monomer and 3D domain-swapped dimer.PMC3443179Zhong NKang XJin CZou PXia BZhang SfalseFoldon unfolding mediates the interconversion between M(pro)-C monomer and 3D domain-swapped dimer.The C-terminal domain (M(pro)-C) of SARS-CoV main protease adopts two different fold topologies, a monomer and a 3D domain-swapped dimer. Here, we report that M(pro)-C can reversibly interconvert between these two topological states under physiological conditions. Although the swapped ?(1)-helix is fully buried inside the protein hydrophobic core, the interconversion of M(pro)-C is carried out without the hydrophobic core being exposed to solvent. The 3D domain swapping of M(pro)-C is activated by an order-to-disorder transition of its C-terminal ?(5)-helix foldon. Unfolding of this foldon promotes self-association of M(pro)-C monomers and functions to mediate the 3D domain swapping, without which M(pro)-C can no longer form the domain-swapped dimer. Taken together, we propose that there exists a special dimeric intermediate enabling the protein core to unpack and the ?(1)-helices to swap in a hydrophobic environment, which minimizes the energy cost of the 3D domain-swapping process.2012-01-01T00:00:00Z2012 Sep2020-11-19T15:54:08Z2019-03-27T00:58:01ZS-EPMC34431792292738810.1073/pnas.1205241109